The present invention relates to electric hygrometers in general, and more particularly to improvements in the manner of and means for supporting the electrolyte in electric hygrometers.
Electric hygrometers are used for determination of relative humidity of gaseous fluids. In such hygrometers, a body of electrolyte is supported between conductors which are connected in circuit with a gauge, a transducer and/or other components of the instrument. The electrolyte is hygroscopic and the impedance between the electrodes is indicative of the relative humidity. The electrolyte is contacted by the electrodes which may constitute portions of the conductors or portions of the supporting or carrier means. For the sake of consistency, the following description of the invention will denote as electrodes those conductive parts which are in actual contact with the electrolyte and through which electric current flows from a conductor to the electrolyte or vice versa, i.e., through which current flows from a first type to a different second type of conductive material.
It is known to measure the relative humidity of air or another gaseous fluid as well as the relative equilibrium humidity of substances other than gases by monitoring the impedance of a hydroscopic electrolyte which is applied to an insulating carrier, e.g., a carrier consisting of glass, ceramic material, textile material, paper or the like. The force with which the electrolyte is held in requisite position depends on the absorbency of the carrier meterial and/or the capillary force. If the electrolyte can be used in solid state, it is often deposited on the carrier means in the form of a thin film or layer.
The hygroscopicity of electrolyte enables the latter to assume a state of water vapor equilibrium with the surrounding atmosphere (air), with another gaseous medium, or with the adjacent stratum or strata of a non-gaseous substance which can absorb water vapors. The electrolyte accepts or releases water vapors until it assumes or reaches a state of equilibrium with the material or substance around it. Of course, it is also necessary to monitor and to take into consideration eventual changes in temperature of electrolyte and/or its carrier means because any deviations of temperature of electrolyte and especially of temperature of the carrier means from the temperature of the surrounding medium greatly affect the accuracy of measurement of relative humidity.
As a rule, the electrodes of presently known hygrometers are applied directly to the carrier means for the electrolyte. Reference may be had to Swiss Pat. No. 382,465. The hygrometer which is disclosed in this patent exhibits a serious drawback, namely, that its reaction to changes in climatic conditions (changes in relative humidity which are normally accompanied by temperature changes) is very slow. The thermal inertia of electrolyte, of electrolyte carrier and of other metallic and/or plastic parts of the patented hygrometer causes a rather long delay between the instant of temperature change and the time when the temperature of component parts of the hygrometer changes sufficiently to conform to the changed temperature of the monitored medium. Consequently, the indications of relative humidity are inaccurate for a certain interval of time in response to each and every temperature change.